replacement display has touch digitizer issues only when out of casing

I got an iPhone SE LCD Screen and Digitizer Full Assembly from iFixit, and

I have replaced the display on my iPhone SE, and the display looks nice, but the touch digitizer is pretty unusable. Tapping is not reliable (typing is almost impossible), and gestures such as swipe or pinch to zoom are very difficult too.

I have done a hard reset (a DFU Restore), just to be sure it wasn't a software or firmware issue, and then I've taken the part off and re-seated the connections a few times, but it hasn't solved the issue. Interestingly, if I reconnect everything (LCD, camera and sensor, and digitizer, and also Touch ID connector), and turn the phone on before I put the display back into the phone casing, then the touch screen works pretty much perfectly. As soon as I set it snugly into its casing where it belongs however, the issue comes back. This is a repeated observation, and I'm reasonably confident now that the issue comes from something touching something when it's fully put together making an electrical connection / grounding that shouldn't be being made.

Here is a video of the behavior I'm describing.

I would insulate something, if I knew what to insulate. Does anybody know?

As @aonemob suggested, I insulated those flex cables (with electrical tape).

BEFORE:

AFTER:

It did improve the responsiveness of the screen, but it still is not perfect, in comparison with a genuine apple touch screen I compared with on another phone. Perhaps the replacement part is just not as high quality.